Based on in vitro and in vivo studies, ATR inhibitors have the potential to treat the following cancers: blood cancers such as leukemia, myeloma and lymphoma; solid tumor such as breast cancer, gastric cancer, prostate cancer, pancreatic cancer, lung cancers (non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC)), colorectal cancer, esophageal cancer, ovarian cancer, neuroendocrine carcinoma, hepatocellular carcinoma (HCC), biliary tract cancer, Ewing’s sarcoma, head and neck squamous cell cancer (HNSCC), soft tissue carcinoma, endometrial cancer, etc. This evidence concerns the gene ATR and head and neck squamous cell carcinoma.